The invention herein relates generally to the art of studying the physical properties of particulate systems and more particularly is concerned with ascertaining accurately the size distribution of particles in a particulate system.
Now well known in the art are apparatuses for measuring a dividing particle size in a particulate system. One such apparatus is shown and described in the above-noted U.S. Pat. No. 3,557,352, hereinafter terms the Mass Median apparatus and Mass Median patent, and can be used to ascertain any particular dividing particle size in a particulate system. The Mass Median apparatus employs a Coulter type particle detector such as shown and described in U.S. Pat. No. 2,656,508. Size in this and the Mass Median patent being synonymous with volume and mass because the particle pulse developed have an amplitude which is proportional to the total solid matter of the sensed particle. Since the material in the particulate system is generally known, its density is known and therefore it is easy to obtain volume by a simple mathematical conversion. Heretofore, the Mass Median apparatus was most often used to ascertain the mass median size of a particulate system which is the 50th mass percentile size. This primary usage is, of course, the basis for the apparatus name. A number of other mass percentile sizes, such as for example the 25th and 75th mass percentile sizes. can be and are determined by the Mass Median apparatus. This information provides a quickly and easily understood description of the nature of the particle distribution. Furthermore, with the information regarding the various mass percentile sizes, a size distribution curve of the particles in the particulate system can be drawn. Such curves are considered extremely useful and important in analyses of particulate systems, and in monitoring of particulate systems where a predetermined particle size distribution is to be maintained. A Mass Median apparatus such as noted above operates under the principle that it is able to measure all particle sizes. Fortunately, in many systems few particles are present which are smaller in size than can be detected by the Coulter type particle detector. In many cases, particles small enough to be undetectable constitute less than 1% of the total particulate system. In using the Mass Median apparatus for analyses of such particulate systems, errors in mass percentile sizes introduced as a result of undetected particles will be minimal.
In many particulate systems however particules are present which are smaller in size than can be detected by a Coulter type particle detector. Representative of such systems are industrial slurries wherein particles vary in size over a great range and include a large percentage of particles which are too small to be detected by a Coulter type particle detector. For purposes of this discussion, 10% is considered to constitute a large percentage of undetectably small particles in a particulate system.
If a particulate system containing for example a total of 10% undetectable particles were passed through a Mass Median apparatus, the sizes indicated by the apparatus for certain mass percentiles would be incorrect and could not be used to derive an accurate distribution curve of the particulate system. Furthermore, the sizes would be of no value in the analysis of the particulate system or in monitoring the particulate system for maintaining a correct particle distribution. Analyzing, monitoring, and maintaining such systems could only be performed after a manual classification and analysis of the particulate system, a tedious, inaccurate and expensive process.